The present invention is directed to an adhesive useful for adhering siliceous containing material to itself or to a substrate. Preferably, the siliceous material or substrate is porous. The substrate can be siliceous or non-siliceous. The adhesives of the present invention are substantially or entirely free of organic solvents since they are aqueous dispersions of polyacrylates mixed with epoxy-silanes wherein the silicon atom of said silane is substituted with hydrolyzable alkoxy groups.
Various adhesives are formed for application to siliceous substrates. The most useful of this particular class of adhesives are the silicones. These materials fall into the one-package type and the two-package type. The one-package type is cured by a reaction induced by water vapor in the atmosphere causing a hydrolysis of groups from a silicon atom. The hydrolyzable groups are generally acetoxy groups or hexylamine groups. The use of these one-package silicones result in the release of acetic acid or hexylamine fumes into the air. Both of these materials have an unpleasant odor. The two-package silicone adhesives give off a much more pleasant odor because the hydrolyzable groups employed results in alcohol fumes being given off. There is however, a necessity for mixing two reactive components to form the adhesive and also the necessity for applying the adhesive to the substrate before it is cured. Another drawback of the silicone adhesives is their low tensile strength. Another deficiency in the silicone adhesive is their release properties. After silicone adhesives are cured, it is very difficult to obtain adhesion to the cured silicone surface. This results in the silicone being very effective as a release coating. This release property results in silicones being undesirable in industries such as the automotive industry since paint will not stick to surfaces which have accidentally come into contact with silicone. Another disadvantage of silicone adhesives is their inability to adhere to wet surfaces. In addition these silicone adhesives are difficult to remove from skin and tools when cleaning up.
Aqueous dispersion type acrylic adhesives again including sealants, on the other hand, have many desirable properties not found in the silicone types. One desirable property is their high tensile strength. Other advantages of aqueous acrylic dispersions in their low odor, and ease of clean-up. Acrylic adhesives of the prior art based upon acrylic dispersions, however, have less than the desirable degree of water insolubility and do not adhere as well as is desired to smooth siliceous substrates such as glass. The adhesion of certain acrylic emulsions used as coatings has in the past been improved by the addition of epoxides. U.S. Pat. No. 2,880,116 of Alps, patented Mar. 31, 1959, discloses formulating an acrylic with an epoxide to improve the adhesion of the coating composition to leather, specifically, and to other materials such as glass, generally. U.S. Pat. No. 3,177,170 of Lund, patented Apr. 6, 1965, also involves the presence of an epoxide and a silicone in a coating composition for glass. The Lund patent, however, involves the use of a volatile organic solvent, an epoxide group on the acrylic polymer and a carboxyl group on the silicone. The Lund patent is not directed to an adhesive composition and has the disadvantage in that its use necessitates the evaporation of aromatic hydrocarbon solvent. Another disadvantage of the Lund system is that heat is required for cure. There are also acrylic caulking compounds on the market which contain epoxy-silanes. These types of caulking compounds are disclosed in U.S. Pat. Nos. 3,759,915 and 3,786,020 of Emmons. They are solvent-based materials.